This invention relates to a battery charging apparatus, and in particular to a battery charging apparatus which displays, during charging, the time to completion when the rechargeable batteries will have reached full charge.
In portable electronic equipment such as camcorders and notebook personal computers, rechargeable batteries are used as the power source. When rechargeable battery power has been consumed by an electronic device, the rechargeable batteries are attached to a charging apparatus and recharged.
The charging apparatus monitors and displays the state of battery charge as the attached rechargeable batteries are charged. For example, as cited in Japanese Non-examined Patent Publication No. 5-283110 issued Oct. 29, 1993 for the case of lithium family rechargeable batteries, the state of battery charge is displayed during charging by monitoring the rechargeable battery voltage up to a specified voltage, and after that by monitoring the rechargeable battery charging current.
Incidentally, displaying the state of battery charge during charging is extremely useful from the rechargeable battery user's perspective. However, it is even more beneficial if the time to the completion of charging for a full charge of the rechargeable batteries is displayed. A system which displays the time to completion of charging is cited in Japanese Non-examined Patent Publication No. 8-298728 issued Nov. 12, 1996. According to this disclosure, the charging voltage characteristic curve and charging current characteristic curve associated with the rechargeable batteries to be charged are pre-loaded into a memory circuit. The rechargeable battery charging current and charging voltage measured by a current sensing circuit and a voltage sensing circuit are related to the pre-loaded charging characteristic curves for calculation of the time to completion of charging by a control circuit. This time to completion is indicated on a display device.
It must be noted that during charging, the charging voltage and charging current characteristic curves are affected and changed by such factors as battery temperature and degree of battery degradation. Consequently, charging current and voltage characteristics measured by the current and voltage sensing circuits become different than the characteristic curves pre-loaded into memory. As a result, an accurate time to completion of charging cannot be calculated.
Therefore, an object of the present invention is to allow for accurate calculation of the time to completion of charging.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.